Presently, there is an increasing interest in developing flexible AM (active matrix) displays for both military and commercial applications. This is at least partially because active matrix display technology provides the potential to realize relatively rugged, full color, lightweight, low power, and low cost flexible displays. Currently, most active matrix displays use rigid glass substrates. Many of these rigid active matrix displays have been, and continue to be, in commercial use in a variety of applications and sizes. For example, relatively small size (e.g., ˜2-inch diagonal) displays have been used in some digital cameras and mobile phones. Relatively large size (e.g., >˜15-inch diagonal) active matrix displays have been used in various other consumer products including, for example, personal computers (PCs) and televisions (TVs).
Although rigid active matrix displays are generally reliable and robust, flexible active matrix displays offer certain potential advantages. For example, flexible active matrix displays may enable many unique display applications, due to the inherent ruggedness and unique form factors of conformability and rollability during use, transportation, and storage. Flexible displays may also be amenable to roll-to-roll manufacturing processes, which may provide significant reduction in manufacturing costs.
Unfortunately, the current processes for fabricating active matrix displays typically are not adequate for the fabrication of active matrix displays using flexible plastic substrates. This is due, at least in part, to the flexible substrate having a CTE (coefficient of thermal expansion) that is significantly larger (˜20 ppm versus ˜3 ppm) than the typical thin films that are used to form thin-film-transistors (TFTs) on the substrate. As a result, thermal stresses may arise, which can lead to curling and warping of the flexible substrate during processing. In most instances, it is not be possible to conduct the various photolithography operations on curled and warped substrates, thereby making it rather difficult, if not impossible, to process the substrate to completion. Moreover, the flexible substrates may shrink during various TFT processing operations, resulting in dimensional instability that may make layer to layer alignment fairly difficult.
Hence, there is a need for a method of fabricating an active matrix display backplane directly on a flexible substrate that does not cause significant thermal stresses in the substrate during TFT processing and/or is relatively dimensionally stable. The present invention addresses one or more of these needs.